Field of the Invention
This present invention relates to a rechargeable electrochemical anion battery cell, which uses a molten salt electrolyte, preferably containing carbonate ion (CO32−).
Related Art
Electrical energy storage is crucial for the effective proliferation of an electrical economy and for the implementation of many renewable energy technologies. During the past two decades, the demand for the storage of electrical energy has increased significantly in the areas of portable, transportation, and load-leveling and central backup applications.
The present electrochemical energy storage systems are simply too costly to penetrate major new markets, still higher performance is required, and environmentally acceptable materials are preferred. Transformational changes in electrical energy storage science and technology are in great demand to allow higher and faster energy storage at the lower cost and longer lifetime necessary for major market enlargement. Most of these changes require new materials and/or innovative concepts with demonstration of larger redox capacities that react more rapidly and reversibly with cations and/or anions.
Batteries range in size from button cells used in watches, to megawatt loading leveling applications. They are, in general, efficient storage devices, with output energy typically exceeding 90% of input energy, except at the highest power densities. Rechargeable batteries have evolved over the years from lead-acid through nickel-cadmium and nickel-metal hydride (“NiMH”) to lithium-ion batteries. NiMH batteries taught, for example, in U.S. Pat. No. 6,399,247 B1 (Kitayama), were the initial workhorse for electronic devices such as computers and cell phones, but they have almost been completely displaced from that market by lithium-ion batteries, taught for example by U.S. Pat. No. 7,396,612 B2 (T. Ohata et al.) because of the latter's higher energy storage capacity. Today, NiMH technology is the principal battery used in hybrid electric vehicles, but it is likely to be displaced by the higher power energy and now lower cost lithium-ion batteries, if the latter's safety and lifetime can be improved. Of the advanced batteries, lithium-ion is the dominant power source for most rechargeable electronic devices.
What is needed is a dramatically new electrical energy storage device that can easily discharge and charge a high capacity of energy quickly and reversibly, as needed. What is also needed is a device that is simple and that can operate for years without major maintenance. It is a main object to provide a new and improved electrochemical battery that is easy to charge and discharge and has low maintenance. One possibility is a rechargeable oxide-ion battery (ROB) set out in U.S. Application Publication No. U.S. 2011/0033769A1 (Huang et al.) and U.S. application Ser. No. 12/850,086 (Huang et al.), filed on Aug. 4, 2010. A ROB comprises a metal electrode, an oxide-ion conductive electrolyte, and a cathode. The metal electrode undergoes reduction-oxidation cycles during charge and discharge processes for energy storage. For example, in discharging mode, the metal is oxidized: yMe+x/2O2=MeyOx and is reduced in charging mode: MeyOx=yMe+x/2O2, where Me=metal.
Molten carbonate fuel cells (“MCFC”) are well known in the art and convert chemical energy into direct current electrical energy, typically at temperatures above about 450° C. This temperature is required to melt carbonate and render electrolyte sufficiently conductive. Alkaline carbonate is a prime electrolyte. Such fuel cells are taught, for example, by U.S. Pat. Nos. 4,895,774 and 4,480,017 (Ozhu et al. and Takeuchi et al, respectively). The general working principles and general reactions of a MCFC are shown in prior art FIG. 1, where anode 12, electrolyte 14, cathode 16 and load 18 are shown, along with the electrochemical reactions. Here, carbon dioxide (CO2) and oxygen (in air, for example) are reduced into carbonate ion (CO32−) by the reaction: CO2+1/2O2+2e−=CO32−. The CO32− migrates to a fuel electrode, anode 12, through a molten carbonate electrolyte 14, and reacts with provided fuel (that is, H2), by the reaction CO32−+H2→H2O+CO2. Therefore, the overall reaction is H2+1/2O2=H2O.
Although a MCFC is able to convert chemical energy of fuel into electrical energy, operated in the temperature range of between 500° C. and 700° C., it is incapable of storing energy by converting electrical energy into chemical energy. Therefore, there is a need to design a rechargeable battery based on carbonate ion for energy storage. This invention describes a rechargeable battery cell in which CO32− is used as a shuttle media to reversibly transport electronic charges between negative and positive electrodes. In addition, the configurations and materials employed in such a battery are also depicted.